1. Field of the Invention
The present invention relates generally to a nonvolatile memory device using a resistance material. More particularly, but not by way of limitation, the invention relates to a nonvolatile memory device having a vertically stacked memory cell array and a repair control circuit that is configured to repair one or more defective memory cells in the array.
2. Description of the Related Art
Generally, examples of a nonvolatile memory device that uses a resistance material include a resistive Random Access Memory (RRAM), a phase change RAM (PRAM), a magnetic RAM (MRAM), and the like. While a dynamic RAM (DRAM) or a flash memory stores data using an electric charge, a nonvolatile memory device that uses a resistance material stores data using a change in resistance of a variable resistive material (RRAM), a change in state of a phase change material (PRAM), such as a chalcogenide alloy, and a change in resistance of a magnetic tunnel junction (MTJ) thin film due to a magnetization state of a ferromagnetic substance (MRAM).
A resistive memory cell includes an upper electrode, a lower electrode, and a variable resistive element interposed therebetween. The resistance level of the variable resistive element varies according to a voltage applied between the upper and lower electrodes. In particular, a filament serving as a current path of a cell current is formed in the variable resistive element. A state where the filament is partially disconnected is defined as a reset state, a high-resistance state, and/or reset data (data 1). A state where the filament is connected is defined as a set state, a low-resistance state, and/or set data (data 0).
When a defect occurs in the nonvolatile memory device (hereinafter, simply referred to as a “defective memory cell”), the defective memory cell may be repaired using a redundant nonvolatile memory cell that has been prepared beforehand (hereinafter, simply referred to as a “redundancy memory cell”). For example, the defective memory cell may be repaired by replacing a word line coupled to the defective memory cell with a redundancy word line coupled to the redundancy memory cell. Alternatively, the defective memory cell may be repaired by replacing a bit line coupled to the defective memory cell with a redundancy bit line coupled to the redundancy memory cell.
Conventional repair circuits for nonvolatile memory devices are lacking in utility, however. For example, conventional repair circuits do not adequately address the needs of nonvolatile memory devices having a vertically stacked memory cell array.